(General biology 



731 



pigment is arranged in a chequered colour pattern, resembling 

 the squares of a chess-board. So regular and characteristic are 

 these stages that, once knowing them, we can separate a young 

 cod from every other young fish, and define its stage of develop- 

 ment or even its age. 



Since Sars discovered the eggs of the cod to be pelagic, a 

 great many other species have been found to possess floating 

 eggs and larvae, for example all the cod-species and flat-fishes, 

 the sprat, the mackerel, and many others. A voluminous 

 literature recording the investigations has accumulated, Agassiz, 



Fig. 521. 



Diagrammatic figures to show the arrangement of the postanal pigment in the eariiest stages of 



CaJiis ca//arias, G. virens, G. pollachius. (After Schmidt. ) 



Ehrenbaum, Heincke, Hensen, Holt, M'Intosh, Masterman, 

 Petersen, and Schmidt having made valuable contributions 

 to our knowledge of the eggs and larvae of various fishes.^ 

 From Schmidt - I reproduce some outline drawings (see Fig. 521) 

 of the pigment arrangement in a corresponding larval stage of 

 three closely related cod-species, viz. Gadus calla7^ias, G. virens, 

 and G. pollachius (the cod, saithe, and pollack). Although 

 these larvae closely resemble each other, the arrangement of 

 the pigment is different. 



^ Ehrenbaum gives an excellent summary in " Eier und Larven von Fischen," Nord. 

 riaiiktoii, Lfg. 4, 1905, Lfg. 10, 1909. 

 - Schmidt, he. cit. 



